Problem sending mail to 2nd SMTP server inside network

I've setup Postfix under Fedora Core 4 using ISPConfig and the "Perfect setup Guide" from this website.

This box is connected directly to the Internet on IP address 70.88.225.1. The mx server information is mail.knifecenter.com at 70.88.225.1.

On my internal network, there is a LISTSERV server. It has an internal IP address of 10.10.1.131. It has an MX record of store.knifecenter.com at 70.88.225.6 (This IP address of 70.88.225.6 is routed to the 10.10.1.131 using NAT routing).

When an e-mail goes to [email protected], it is routed perfectly. The listserv works flawlessly, both receiving and sending messages.

However, when a message is sent to [email protected] from WITHIN our network, the following error message occurs:

I found the solution! It's a simple one, but I guess noone knew exactly what I was talking about.

Basically, I needed to NIC cards: one to communicated directly within the network and a second one to connect directly to the internet. With this solution, I still maintain connectivity with the internal network (file sharing, etc.) and also avoid the problem of not being able to send internet mail from within the network.

falko said:

Is it maybe a problem with your router not allowing loopbacks into your network?
Or maybe a firewall setting?